Hydrofoil craft



Dec. 11, 1956 o. z. BAILEY HYDROFOIL CRAFT 4 Sheets-Sheet 1 Filed Jan.9, 1952 8 INVENTOR.

Dqvid Z. Bailey BY 04m, yuan/r45 M &4?

TT EYS Dec. 11, 1956 D. 2. BAILEY 2,773,467

HYDROFOIL CRAFT Filed Jan. 9, 1952 4 Sheets-Sheet 2 v INVENTOR. David Z.Bailey BY ofawz yowwtclawdafi @440 ATTORNEYS Dec. 11, 1956 D. z. BAILEY2,773,467

HYDROFOIL CRAFT Filed Jan. 9, 1952 4 Sheets-Sheet 3 40b FIG.4

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INVENTOR. .Dovid Z. Bailey BY v Warm/ 70W aadc/flcwo ATTORNEYS UnitedStates Patent HYDROFOIL CRAFT David Z. Bailey, Charlestown, R. I.Application January 9, 1952, Serial No. 265,551 7 Claims. (Cl. 114-66.5)

This invention generally relates to the control of Iongitudinalstability of water craft utilizing hydrofoil support for the purpose ofreducing skin friction and displacement drag by raising the hull of thecraft to a higher position with respect to the surface of the Water inwhich it travels. In a more particular aspect, this invention concernsnot only control of longitudinal stability but also control of lateralstability.

A hydrofoil is a submerged surface mounted beneath the underside of awater-borne craft which provides an upward force component or lift whenthe craft has forward velocity with respect to the Water. If thevelocity of the craft with respect to Water is sufficiently high, thelift exerted on the hydrofoil by the water may be sufficient to raisethe entire hull above the surface of the Water, which is the desiredform of travel for hydrofoil craft.

Hydrofoil craft are subject to certain disadvantages which are caused bythe ever disturbed condition of the surface of almost every body ofwater. At a constant velocity of the craft with respect to the water,the lift force is a function of the angle of attack of the hydrofoil, i.e. angle between the water streamline and the chord line of thehydrofoil. Waves and similar disturbances produce changes in the angleof attack and the consequent change in lift tends to cause the craft toride over the Waves and to maintain a constant height above the surface.Such variations in angle of attack result in highly inefficientoperation of the hydrofoil from a hydrodynamic standpoint since they mayresult in stalling as Well as in wasted power in constantly raising andlowering the craft.

Moreover, the response of the craft to the surface configuration isalways somewhat delayed, and therefore the upward reaction of the craftto a wave crest might raise the hydrofoil so near the surface of thefollowing wave trough as to cause ventilation and serious loss of lift.Loss of lift can occur whenever the hydrofoil comes so close to thewater surface that the flow of water over the hydrofoil tends to disturbthe water surface.

My invention concerns principally a short period control system forhydrofoil boats which is designed to offset the effect of waves andsimilar disturbances sothat the craft tends to ride along an even leveland so that the.

supporting hydrofoil maintains a constant angle of attack With thestreamline. In a more particular aspect my invention also permits a longperiod control system for depth regulation which operates independentlyof the short period system to maintain or adjust operation to a selectedmean depth. The long period system advantageously is laterally dividedto provide independent control for port and starboard and thus alsoprovide lateral stability.

In order to secure these ends, I provide in addition to the mainhydrofoil a secondary or control hydrofoil mounted beneath the undersideof the craft and free to assume an approximately streamline path bothvertically and in pitch angle. The control hydrofoil is directly con-Patented Dec. 11, 1956 nected to the main hydrofoil so that the pitchangle of the main hydrofoil correspondingly ,and equally reflectschanges in the pitch angle of the control hydrofoil induced by changesin the direction of flow of water past the control hydrofoil (shortperiod system). In addition,

Figure 3 is an enlarged view of a control system ofan- 7 other craftidentical to that shown in Figure l but also utilizing a system forcontrolling lateral stability coordinated with the long period stabilitycontrol system.

Figures 4, 5, 6, 7, 8 and 9 describe a third craft identical to that inFigure 3, but also utilizing a system forvarying the lift coefiicient ofthe main hydrofoil.

Figure 4 is a plan view of a portion of the control system, whileFigures 5 andv 6 are sectional elevations of the apparatus shown inFigure'4 taken along lines 5-5 and 6-6, respectively.

Figure 7 is a horizontal section of another portion of the third'craft,while Figure 8 is a vertical section of the apparatus shown in Figure 7taken along line 8--8 in Figure 7. Figure 9 is a front view shownpartially in section of the apparatus shown in Figures 7 and 8 taken atline 9-9 in Figure 8.

Referring to Figures 1 and 2 of the drawings, the reference numeral 1represents a hydrofoil water craft embodying a simple illustration of myinvention. Hydrofoil craft 1 comprises a hull 2 of conventional shapehaving mounted thereon, by means of hollow supporting strutsv 3 andhorizontal beam 4, a main hydrofoil 5. Struts 3' and hydrofoil 5 are ofstreamline cross-section so as to reduce frictional drag through thewater as much as possible. Hydrofoil 5 is pivoted to struts 3 at points6.

. The craft is provided with a rudder assembly 7 comprising a tiller 8,strut rudder 9 and stabilizer hydrofoil 10. Preferably, stabilizerhydrofoil 10 is of adjustable pitch angle, by means of sheave 11 andline 12 which is,

streamline cross-section passes downwardly through an aperture 14 incraft 1 and terminates at its lower end below the underside of thecraft 1. Control hydrofoil 15 is mounted in front of strut 13 by leverarm 16 which is fixed at end 17 to control hydrofoil 15 and pivoted tostrut 13 at point 18 intermediate the length of arm 16.

Strut 13 is supported by a second lever arm 19 lying in the samevertical plane as, and parallel to, lever arm 16. Lever arm 19 ispivotally mounted to craft 1 at point 20 and is pivotally connected tothe upper portion of strut 13 at point 21 intermediate the length of arm19. A third lever arm 22, lying in the same vertical plane as, andparallel to, lever arms 16 and 19, is pivotally connected at its end 23with strut 13. The pivot point 23 lies on the imaginary line determinedby points 21 and 18. Lever arm 22 is pivotally connected at its otherend with craft 1 at point 24A which is determined by the point ofintersection of arm 22 With an imaginary line passing through point 20parallel to the imaginary line determined by points 21 and 18. The freeends 24 and 25 of lever arms 19 and.16, respectively, are linked byconnecting rod 26 which is parallel to the imaginary line determined bypoints 21 and 18. Lever arm 19 is connected at point 20 by direct axleconnection with sheave 27. The length of lever arm 16 from pivot point25 to the forward tip of control hydrofoil 15 must be substantially lessthan the distance on lever arm 19 between pivot points 20 and 24.

The pitch of hydrofoil is controlled by cable 28 which is wound oversheave 29 mounted to beam 4 and is fastened to hydrofoil 5 at point 30on the leading surface point 31 on the trailing surface. Preferably, thesheave and line arrangement is duplicated at each end of hydrofoil 5.Cables 28 pass down through the centers of hollow struts 3. Sheaves 29are mounted on a common axle '32 which traverses beam 4 of craft 1.Sheave 33 is mounted on axle 32 in line with sheave 27 and has adiameter twice that of sheave 27. Forward of sheave 33 and in line withit is positioned sheave 34 which is suitably mounted to the deck ofcraft 1 and which is rotatable by crank 35.

Cable 36 attached to pulley block 37 and pulley block 38 passes aroundsheave 27. A continuous cable 39 is passed from the. underside of sheave33 to the underside of pulley sheave 40 mounted in pulley block 37, fromthe upper side of pulley sheave 40 to the underside of sheave 34, fromthe upper side of sheave 34 to the underside of pulley sheave 41 mountedin pulley block 38 and from the upper side of pulley sheave 41 to theupper side of sheave 33.

Figure 2 illustrates more clearly the mechanism by which the controlhydrofoil operates to vary the pitch angle of main hydrofoil 5.

If, for example, there is a downward velocity of the boat or an upwardvelocity of the water due to some disturbance such as the crest of aWave passing control hydrofoil 15, then there is an increase in lift oncontrol hydrofoil 15 because the effective angle of attack of thecontrol hydrofoil is increased. The added lift will cause controlhydrofoil strut 13 to rise with respect to the boat thereby causinglever arms 22 and 19 to rotate about their forward pivots 24A and 20,respectively. By means of connecting rod 26, lever arm 16 is made torotate in a similar manner and to decrease the angle of attack untilhydrofoil 15 assumes a new equilibrium position with respect to thewater flowing past it. Such equilibrium position is, of course,approximately a streamline position with just sufficient angle of attackto exert enough lift to support the free weight of strut 13 and itsassociated lever arm mechanism. The dotted line position in Figure 2illustrates such a new equilibrium point caused by a downward velocityof the boat or an upward velocity of the water. It will be observed thatinherently the movement imparted to control hydrofoil 15 by itssupporting structure, as hydrofoil 15 moves from one equilibriumposition to another in following a streamline path, is about a pivotaxis which extends horizontally and which is located forward of controlhydrofoil 15 transversely passing through the intersection A of animaginary line through pivots and 24a with an imaginary line passingthrough pivots 18 and 25.

The movement of lever arm 19 in response to such changes in theequilibrium position of hydrofoil 15 causes sheave 27 to rotate, whichrotation is translated into a change of position of pulley blocks 37 and38 by means of cable 36. In ordinary operation crank 35 is secured inone position so that sheave 34 remains stationary. Hence, the movementof pulley blocks 37 and 38 causes a corresponding rotation in sheave 33due to the movement of cable 39 induced by such change in position ofpulley blocks 37 and 38. Since sheave 33 has twice the diameter ofsheave 27, it is displaced through an angular change equal to theangular displacement of sheave 27. Sheave 33 causes sheaves 29' torotate equally since they are connected by common axle 32' and thus themotion of hydrofoil 15 is communicated directly and equally to hydrofoil5, thus causing its lift to, decrease,

thereby tending to offset the effect of the downward velocity of thecraft or upward velocity of the water which induced the change inposition of hydrofoil 15 and to maintain hydrofoil 5 at a constant angleof attack with the streamline.

However, the short period system which I have just described is notcomplete. I have found it is also necessary to provide a mechanism forindependently adjusting to new boat velocities or to allow for verticalaccelerations. In addition, the boat might slowly sink or rise due toinability of a small change in lift on the control hydrofoil 15 to movethe control system because of the friction in the system. When it isdesired to change the vertical position of the craft with respect to thewater, it is necessary to rotate main hydrofoil 5 while maintainingcontrol hydrofoil 15 in the same position. This is accomplished byproviding an independent mechanism for adjusting the pitch angle of mainhydrofoil 5 without affecting the pitch angle of control hydrofoil 15.That is, a means is provided to adjust the phase relation between thepitch angles of control hydrofoil 15 and main hydrofoil 5.

In the craft illustrated in Figures l and 2 such an independent controlmechanism is crank 35 and sheave 34 which are coordinated with theoperation between sheaves 27 and 33 by pulleys 37 and 38. Thus, changingthe position of crank 35 causes sheave 34 to rotate. Such rotation istranslated to sheave 33 and thereby to main hydrofoil 5. The position ofcontrol hydrofoil 15, of course, is entirely independent of suchoperation and is not elfected by it.

The long period system, that is, the independent control of the phaserelation between the pitch angles of the control and main hydrofoils, ismore usefully controlled by automatic rather than by human response.While the pilot is able to control the craft shown in Figure l, theadjustment of crank 35 is difficult at best. Moreover, the pilot willnot always react fast enough and will have difliculty in judging thedegree of correction needed.

It is best, therefore, in the interests of safety to effect the changein pitch angle relation by utilizing a conventional depth senser whichmeasures the depth at the hydrofoil or some other convenient point basedon the conversion of hydrodynamic energy into electrical energy. Forexample, a Pitot static tube with static pressure holes advantageouslyis arranged with a resistance type strain gauge (or a slide wire andpiston) so that the resistance of the strain gauge is a function of thestatic pressure at the holes. An electrical control circuit is governedby the strain gauge and is adjusted so that operation may be set for anydesired actual depth at the point of measurement. The electrical controlcircuit is used to energize a motor which is geared to drive sheave 34in accordance with deviations from the desired depth.

It should be noted that the short period system not only remainsunaffected by changes in the phasing of the pitch angles of mainhydrofoil 5 and control hydrofoil 15, except insofar as such changes maymomentarily require a readjustment of control hydrofoil 15 to a newequilibrium position, but also hydrofoil 15 is only negligibly affectedby the pitching moment of hydrofoil 5 since pivot points 6 are locatedapproximately at the ends of the theoretical line across the span ofhydrofoil 5 about which all force components are exerted, thus thereaction load is carried principally by pivot points 6, and since aconsiderable mechanical advantage exists between hydrofoil 15 andhydrofoil 5.

The utilization of such a long period system facilitates control oflateral stability as Well as longitudinal stability. That is, the mainhydrofoil may be divided by a central strut into two sections eachindependently controlled for desired depth by a Pitot tube located atthe lower end of the adjacent outside strut. Each main hydrofoilcontinues to be controlled in the same degree by the control hydrofoil.

Figure 3 is a close-up view of the central portion of a hydrofoil craftsimilar to that shown in Figure 1 but which also utilizes a system oflateral stability control. In the figure, the parts not shown areidentical with those in Figure 1. Where I have used the same numbers, itis to be understood that the same part is intended. Also in thedesignation of the parts I have utilized the suffix a to designate allthe parts which are specific to the port side of the craft and thesuflix b to designate all the parts specific to the starboard side ofthe craft where such parts are symmetrically disposed on both port andstarboard.

It will be noted that the craft illustrated in Figure 3 utilizes anidentical control system as the craft shown in Figure 1. However, frompulley blocks 37' and .38 to hydrofoils 5a and 5b the system is dividedinto two corresponding halves, each half corresponding in operation tothe operation between pulley blocks 37 and 38 and hydrofoil 5 of craft 1in Figure 1. Craft 1' is provided with a central strut 3 which dividesmain hydrofoil 5 into two sections 5a and 5b. The use of the centralstrut permits control of. each main hydrofoil 5a and 512 by passingcables 28a and 281; through the central strut rather than requiring theneed of an axle 32 and additional sheaves 29 as in Figure 1.

Pulley blocks 37' and 38 each carry a pair of pulley sheaves, 40a and40b, and 41a and 41b, respectively. Sheave 34 of Figure 1 is replaced bytwo independently mounted sheaves 34a and 34b which are driven byelectric motors 42a and 4212 through screw drive transmissions 43a and43b, respectively. Motors 42a and 42b are controlled by the hydrostaticpressure at Pitot static tubes 44a and 44!), respectively, mounted instruts 3. Sheave 33 of the craft in Figure 1 is replaced by a pair ofindependently mounted double grooved sheaves 45a and 45b.

Continuous cables 39a and 3% are substituted for single cable 39 of thecraft in Figure 1. Thus cable 39a traverses sheave 45a, pulley sheave40a, sheave 34a and pulley sheave 41a in the same manner that cable 39traverses sheave 33, pulley sheave 40, sheave 34 and pulley sheave 41,respectively, in Figure 1. Cable 39b is correspondingly mounted aboutsheave 45b, pulley sheave 40b, sheave 34b and pulley sheave 4111,respectively. Cables 28a and 28b attached to hydrofoils 5a and 5b,respectively, are passed through the second groove of sheaves 45a and4512, respectively, and are housed within hollow center strut 3.

As the craft is passing through the water, disregarding for the momentthe operation of the two long period control systems, any change inposition in control hydrofoil 15 is transmitted to pulley blocks 37 and38' as in the operation of the craft in Figure 1. So long as the twolong period systems are inoperative, sheaves 34a and 34b remainstationary and therefore hydrofoils 5a and 5b are caused to change theirpitch angle in exactly the same amount as control hydrofoil 15 ischanged by whatever disturbance moves it.

However, as soon as either side of the craft changes in depth from thedesired and selected depth of operation, the change in static pressureof the Pitot static tube energizes operation of its correspondinglateral control system. For example, assume that the port side of craft1 sinks due to a change in the loading of the craft, the increase inhydrostatic pressure measured at Pitot tube 44a causes motor 42a to turnsheave 34a so as to increase the pitch of hydrofoil 5a in the samemanner that rotation of sheave 34 changes the pitch in the craft inFigure l, and thus returns craft 1 to an even keel, motor beingde-energized when the desired depth is again attaiued. This same action,of course, is eifective on both port and starboard and operates tomaintain the craft on an even keel as well to control the desired depthof operation as in Figure 1. During turning operations the pilot canchange the desired depth for each side todifferent values and thusobtain the necessary bank for turning.

The same type of long'period control system may be coordinated. to varythe mean camber of the hydrofoil. Figures 4, 5, 6, 7, 8 and 9 illustratea modification of the device shown in Figure 3 for effecting such achange in mean camber of the main hydrofoils. Where I have used the samenumbers, the same parts are intended as in Figures 3 and 1, and theiroperation will be identical with that of the operation in Figure 3.Also, the use of the subscripts a and b has been retained with the samemeaning as in Figure 3.

Referring first to Figures 7, 8 and 9 to illustrate the change inhydrofoil structure, it will be noted that Figure 8 is a cross-sectiontaken through hydrofoil 5'a looking toward center strut 3'. Hydrofoil 5ais divided spanwise into two principal sections. Main span 46a is awedge shaped piece extending through three-quarters of the cord line ofhydrofoil 5a. The first quarter of hydrofoil 5a is a sharp pointedcircular arc nose flap 47a. Leading edge (nose flap) 47a is movablyfixed to main span 46a by spring steel strip 49a and stretched rubberstrip 48a.

Referring now to Figures 4, 5 and 6 which illustrate the adjustment inthe pulley system to accommodate a control system of the flap angle, itwill be seen that the system of Figure 3 has been duplicated. However,an additional pair of symmetrically disposed systems have been added, sothat each pulley block 37" and 33 now carries 4 pulley sheaves insteadof 2 as in Figure 3. To motor driven sheaves 34a and 34b have been addedadditional sheaves 51a and 51b, respectively, of three times thediameter of sheaves 34a and 3411. Double grooved sheaves a and 45b havebeen combined with additional elements to produce compound sheaves a and50!), respectively Sheave 50a, working from inside out, comprises doublegrooved sheave 45a which is axially mounted to rotate freely, grooveedged plate 57a which is pivotally connected on pin 58a with sheave 45a,link 59a which is pivotally connected with plate 57a by pin 60a, andoutside sheave a which is pivotally connected to link 5911 by pivot pin61a. Outside sheave 56a is single grooved, is axially mounted to rotatefreely, and is of the same diameter as sheave 45a. The distance of pivotpin 58a from the center of sheav 45a is equal to the distance betweenpivot pins a and 61a on link 59a. The distance of pivot pin 61a from thecenter of sheave 5'6a is equal to the distance between pivot pins 58aand 60a on plate 57a. Sheave 50b is, of course, the symmetricalcounterpart of sheave 50a.

In the cable and pulley connection arrangement cable 54a is continuousand passes from the bottom of sheave 56a to the bottom of pulley sheave52a, from the, top of pulley sheave 52ato the top of sheave 51a, fromthe bottom of sheave 51a to the bottom of pulley sheave 53a and from thetop of pulley sheave 53a to the top of sheave 56a.

Figure 4 is an elevation view of the arrangement of all four cables 39:!and 39b, and 54a and 54b. Figure 5 is a cross-section taken along line55 in Figure 4 and shows exclusively the arrangement of cable 54a whichis a duplicate of the arrangement of cable 54b. In Figure 5 sheave 56ais partially cut away to show the internal arrangement of compoundsheave 50a.

Figure 6 is a section through Figure 4 along line 6-6 and showsexclusively the arrangement of cable 3%. In Figure 6 double sheave 45bis partially cut away to show the internal arrangement of parts incompound sheave 50b which in all respects is a mirror image of sheave50a.

Control cables 28a and 28b which control main hydrofoil spans 46a and461') are wound over the second grooves of sheaves 45a and 45b,respectively, and pass down through central strut 3'. Control cables 62aand 7 62b which adjust the flap angles of flaps 47a and 47b,respectively, pass over grooved plates 57a and 57b, respectively, andalso are fed downwardly through central strut 3.

Referring now to Figures 7, 8 and 9, it will be noted that main span 46ais bolted to a plate 55a and pivoted on pin 63 to strut 3. Span. 46b issimilarly pivoted. Cables 28a and 28b are fastened to the ends of plates55a and 55b, respectively, and thus translate the motion of controlhydrofoil 15 to the main span hydrofoils 46a and 46b as before (Figure 3Flap angle control cables 62a and 62b are connected to the ends ofplates 64a and 64b, respectively, which are bolted at their forward endsto nose flaps 47a and 47b and are pivoted on pins 65a and 65b to plates55a and 551;, respectively, the point of pivot being adjusted in theillustrated case at the quarter cord distance and along the uppersurface of the foil.

Referring back to Figures 4, and 6, for the moment, each of groovedplates 57:: and 57b is formed having opposite arcuate edges about pivotpins 58a and 58]), respectively, as centers. Each of pivot pins 58:: and58b is located in its respective plate 57a or 57b so that one sucharcuate edge is constructed with three times the radius of the oppositearcuate edge. Thus the por tion of each of cables 62a and 6212 leadingto the forward edge of each of plates 64a and 64b, respectively, will bemoved through onethird the distance through which the other end of thecable moves, as each of plates 57a and 57b is rotated about pivot pin58a and 5811, respectively. It will be apparent that each of plates 57aand 57!) has the same angular geometry as each of plates 64a and 65b,and thus angular motion about pivot 58a or 58b is duplicated about pivot65a and 65b, respectively, while angular motion about the central axesof sheaves 50a and 56b is duplicated about pin 63.

In operation, when the long period control system is stationary, it willbe seen that any motion in hydrofoil 15 is directly translated equallyto both main spans 46a and 46b of hydrofoils 5a and 5b. By the samemotion each of sheaves 56a and 56b will be caused to move through thesame angle of rotation as double sheaves 45a and 45b and hence plates57a and 57b will also exhibit the same degree of turn about the axiallines of sheaves 56a and 45a, and 56b and 45b, respectively. Sinceplates 57a and 57b rotate through the same angle as sheaves 45a and 45band sheaves 56a and 56b, re spectively, and since cables 62a and 62])are substantially parallel to cables 28a and 28b, the flap deflectionangle of hydrofoils 5a and 5b remains substantially constant.

However, when the long period system of either side is caused tooperate, due to the geometry of the system, the flap angle is giventhree times the effect and in an opposite direction as the mainhydrofoil span. Assume, for example, that it is desired to increase thelift of hydrofoil 5a, this is done by increasing its angle of attack byenergizing motor 42a which causes its associated sheaves 51a and 34a torotate at a slow rate of speed. Assuming that control hydrofoil 15remains in a stationary position, this rotation will cause cable 54:: torotate three times as much as cable 390 since sheave 51a has three timesthe diameter of sheave 34a. Moreover, the movement of the cables 39a and54a will be in opposite directions. Since the geometry of plate 57a issuch that it is pivoted with respect to sheave 45a at the same relativepoint as nose flap plate 64a is with respect to main span plate 55a, theopposite and threefold angular rate of movement induced in plate 64::will cause nose flap 47a to be deflected downwardly with a flapdeflection three times as great as the increase in pitch of span 460.

It will be obvious to those skilled in the art that certain changesother than those I have suggested may be made in the described watercraft. For example, hydrofoil 15 may be positioned aft of strut 13. Itsoperation will produce identical results. However, it should beremembered that the water disturbance created by strut 13 will, in adegree, reduce the sensitivity of hydrofoil 15. For that matter,hydrofoil 15 can be placed with its associated support mechanism aft ofthe main hydrofoil. The same objections however can be made against thedesirability of such practice. One convenient alternative arrangement isto place strut 13 and connecting rod 26 inside central strut 3' with aslit .in the leading edge of strut 3' to allow lever arm 16 to move upand down hold ing hydrofoil 15 out ahead.

The pulley assemblies above decks may readily be replaced by equivalentmechanical linkages, for example, by cranks and a connecting rod havingan adjustable connection such as a slidable pivot point. Or lever arm 19might turn an axle which drives the rotor of a selfsynchronous motorhaving its stator connected in parallel to the stator of anotherself-synchronous motor, both having their rotors connected to a commonA. C. supply, which second motor would be used to drive axle 32. Or anangularly responsive electrical mechanism, such as a self-synchronoustransmitter, might be positioned at pivot point 25 utilizing a seWomechanism to produce equal changes in hydrofoil 5, or hydrofoils 5a and5b, as the case may be. In such cases, phase adjustment could be madeeither electrically by known methods or by a mechanical system involvinga transmission and clutch. Along the same idea the pulley and cablearrangements of the craft shown in Figure 3 and of the craft shown inFigures 49 may be substituted by obvious mechanical and electricalequivalents.

It will be noted that I have omitted any description of a propulsionsystem. I contemplate the use of any of the marine propulsion systemsutilized in hydrofoil type craft. In particular, air propulsion isextremely well adapted to hydrofoil craft as it provides minimumdisturbance of the water passing the hydrofoils.

I claim:

1. In a water craft having a main hydrofoil pivotally supported belowthe level of the underside of the craft which hydrofoil is inclinable toprovide an upward force component by dynamic action with the water whenthe craft has forward velocity with respect to the water, theimprovement which comprises a control hydrofoil; an approximatelyvertically positioned strut passing downwardly through the craft, freeto move in approximately vertical directions with respect to the craft,and terminat ing at its lower end beneath the underside of the craft; afirst lever arm lying in approximately the fore and aft direction ofsaid craft, fixed at one end to said control hydrofoil, and pivotallyconnected at a point intermediate its length with the lower end of saidvertical strut; a second lever arm lying in the same vertical plane as,and parallel to, said first lever arm, pivotally connected at one endwith said craft, and pivotally connected at a point intermediate itslength with the upper portion of said vertictal strut; a third lever armlying in the same vertical plane as, and parallel to, said first andsecond lever arms, pivotally connected at one end with said verticalstrut along the imaginary line determined by the pivotal connections ofsaid first and second lever arms with said strut, and pivotallyconnected at its other end with said craft at the point determined byits intersection of the imaginary line passing through the pivotalconnection of said second lever arm with said craft parallel to theimaginary line determined by the pivotal connections of said first andsecond lever arms with said strut; a connecting rod parallel to theimaginary line determined by the pivotal connections of said first andsecond lever arms with said strut, and pivotally connected at its endswith the free ends of said first and second lever arms; linkageconnecting said control hydrofoil and said main hydrofoil, wherebychanges induced in the angular position of said control hydrofoil arereflected by corresponding changes in the angular position of said mainhydr0- foil; and means independent of the angular position of saidcontrol hydrofoil for varying the phase relation of the angularpositions of said control and main hydrofoils. I 2. In a water crafthaving a mainvhydrofoilpivotally supported below the level of theunderside of the craft 10 strut, and pivotally connected at itsotherendwithsaid craft at the point determined by its'intersection of theimaginary linepassingithrough'the pivotal connection of said second leverarm with saidcraftparallel to the imaginary line determined by thepivotal connections of said first and second lever arms with said strut;a connecting rod paral which hydrofoil is inclinable to provide an upward force component by dynamic action with the water when the craft hasforward velocity with respect to the Water and which main hydrofoilisdivided into an independent port hydrofoil and an independent starboardhydrofoil; the improvement which comprises a control hydrofoil; anapproximately vertically positioned strut passing downwardly through thecraft, free to move in approximately vertical directions with respect tothe craft,'and'terminat ing at its lower end beneath the underside ofthe craft; a first lever arm lying in approximately the fore and aftdirection of said craft, fixed at one endto said control hydrofoil, andpivotally connected at a point intermediate its length with the lowerendofsaid'fvertical strut; a second lever arm lying in the same verticalplane as, and parallel to, said first lever arm, pivotally connected atone end with said craft, and pivotally connected at a point intermediateits length Withthe .upper portion of said vertical strut; a third leverarm lying in the same vertical plane as, and parallel to, said first andsecond lever arms, pivotally connected at one end with said verticalstrut along the imaginary line determined by the pivotal connections ofsaid first and second lever arms with said strut, and pivot-allyconnected at its other end with said craft at the point determined byits intersection of the imaginary line passing through the pivotalconnection of said second lever arm with said craft parallel to theimaginary line determined by the pivotal connections of said first andsecond lever arms with said strut; a connecting rod parallel to theimaginary line determined by the pivotal connections of said first andsecond lever arms with said strut, and pivotally connected at its endswith the free ends of said first and second lever arms; linkageconnecting said control hydrofoil and each of said main hydrofoils,whereby changes induced in the angular position of said controlhydrofoil are reflected by corresponding changes in the angularpositions of each of said main hydrofoils; and a pair of meansindependent of the angular position of said control hydrofoil, one forvarying the phase relation of the angular positions of said control andsaid port main hydrofoils, and the other for varying the phase relationof the angular positions of said control and said starboard mainhydrofoils.

3. In a water craft having a main hydrofoil pivotally supported belowthe level of the underside of the craft which hydrofoil is inclinable toprovide an upward force component by dynamic action with the Water whenthe craft has forward velocity with respect to the water and which mainhydrofoil is divided into an independent port hydrofoil and anindependent starboard hydrofoil; the improvement which comprises acontrol hydrofoil; an approximately vertically positioned strut passingdownwardly through the craft, free to move in approximately verticaldirections with respect to the craft, and terminating at its lower endbeneath the underside of the craft; a first lever arm lying inapproximately the fore and aft direction of said craft, fixed at one endto said control hydrofoil, and pivotally connected at a pointintermediate its length with the lower end of said vertical strut; asecond lever arm lying in the same vertical plane as, and parallel to,said first lever arm, pivotally connected at one end with said craft,and pivotally connected at a point intermediate its length with theupper portion of said vertical strut; a third lever arm lying in thesame vertical plane as, and parallel to, said first and second leverarms, pivotally connected at one end with said vertical strut along theimaginary line determined by the pivotal connections of said first andsecond lever arms with said lel to the imaginary line determined byv thepivotal con-v nections 'of said first and second lever arms with saidstrut, and pivotally connected at its ends with the free ends of saidfirst and second lever arms; linkage connecting said control hydrofoiland each of said main hydrofoils, whereby changes induced inthe angularposition of said control hydrofoil are reflectedby corresponding changesin the angular positions of each of said main hydrofoils; a first pairof means independent of the angular position of said, control hydrofoil,one for varying the phase relation of the angular positions of saidcontrol and said port main hydrofoils, and the other for varying thephase relation of theangular positions of said con-. trol andsaidstarboard main hydrofoils; and a second pair of means independent ofthe angular position of said control hydrofoil, coordinated with saidfirst pair, one

for varying the mean camberof said port main hydrofoil, and the otherfor varying the mean camber of said,

starboard main hydrofoil.

4. In a water craft having a main hydrofoil pivotally supported belowthe level of the underside of the craft which hydrofoil is inclinable toprovide an upward force component by dynamic action with the water whenthe craft has forward velocity with respect to the water; theimprovement which comprises a control hydrofoil; means supporting saidcontrol hydrofoil below the level of the underside of the craft, saidcontrol foil being movable about a horizontally extending pivot axisforward of said control foil whereby said control hydrofoil assumes anapproximately streamline path through the water beneath the surfacethereof when said craft has forward velocity with respect to the water;linkage connecting said control hydrofoil and said main hydrofoil,whereby changes induced in the angular position of said controlhydrofoil are reflected by corresponding changes in the angular positionof said main hydrofoil; and means independent of the angular position ofsaid control hydrofoil for varying the phase relation of the angularpositions of said con-trol and main hydrofoils.

5. In a water craft having a main hydrofoil pivotally supported belowthe level of the underside of the craft which hydrofoil is inclinable toprovide an upward force component by dynamic action with the water whenthe craft has forward velocity with respect to the water and which mainhydrofoil is divided into an independent port hydrofoil and anindependent starboard hydrofoil; the improvement which comprises acontrol hydrofoil; means supporting said control hydrofoil below thelevel of the underside of the craft, said control foil being movableabout a horizontally extending pivot axis forward of said control foilwhereby said control hydrofoil assumes an approximately streamline paththrough the water beneath the surface thereof when said craft hasforward velocity with respect to the water; linkages connecting saidcontrol hydrofoil and each of said main hydrofoils, whereby changesinduced in the angular position of said control hydrofoil are reflectedby corresponding changes in the angular positions of each of said mainhydrofoils; and a pair of means independent of the angular position ofsaid control hydrofoil, one for varying the phase relation of theangular positions of said control and said port main hydrofoils, and theother for vary-ing the phase relation of the angular position of saidcontrol and said starboard main hydrofoils.

6. In a water craft having a main hydrofoil pivotally supported belowthe level of the underside of the craft which hydrofoil is inclinable toprovide an upward force component by dynamic action with the water whenthe craft has forward velocity with respect to the water and which mainhydrofoil is divided into an independent port hydrofoil and anindependent starboard hydrofoil; the improvement which comprises acontrol hydrofoil; means supporting said control hydrofoil below thelevel of the underside of the ,craft, said control foil being movableabout a horizontally extending pivot axis forward of said control 'foilwhereby said control hydrofoil assumes an approximately streamline paththrough the water beneath the surface thereof when said craft hasforward velocity with respect to the water; link-ages connecting saidcontrol hydrofoil and each of said main hydrofoils, whereby changesinduced in the angular position of said control hydrofoil are reflectedby corresponding changes in the angular positions of each of said mainhydrofoils; and a pair of means independent of the angular .position ofsaid control hydrofoil, one for varying the phase relation of theangular positions of said control and said port main hydrofoils, and theother for varying the .phase relation of the angular position of saidcontrol and said starboard m-ainhydrofoils; and a second pair of meansindependent of said control hydrofoil coordinated with said first pair,one for varying the mean camber of said port main hydrofoil and theother for varying the mean camber of said starboard main hydrofoil.

7. f lm afwater craft having a main hydrofoil pivotally supported belowthelevel of the underside of the craft; the improvement which comprisesa control hydrofoil; means supporting said control hydrofoil below thelevel of the underside of the craft, said control foil being movableabout a horizontally extending pivot axis forward of said control foilwhereby said control hydrofoil assurnes an approximately streamline.path through the water beneath the surface thereof when said craft hastor-ward velocity with respect to the water; and linkage connecting saidcontrol hydrofoil and said main hydrofo'i'l, whereby changes induced inthe angular position of said control hydrofoil are reflected bycorresponding changes in the angular position of said main hydrofoil.

References Cited in the file of this patent UNITED STATES PATENTS1,186,816 Meacham June 13, 1916 2,387,907 Hook Oct. 30, 1945 2,584,347Hazard v Feb. 5, 1952 2,603,179 Gardiner July 15, 1952 FOREIGN PATENTS516,651 Great Britain J an. 8, 1940

